Metal has been used to enhance the burning rate of solid propellant compositions. The metal has been added to uncured solid propellant compositions in various forms, e.g., ribbons, powder, staples, spheroidal, and other geometric shapes.
Metallic compounds in the forms of ferrocenes or carboranes have also been used as burning rate enhancers. Examples of each of these compounds are n-butylferrocene and n-hexylcarboranes. Derivatives of ferrocenes and carboranes have been employed. An example of a very expensive ferrocene derivative is known as Catocene, the registered trademark for Syntex Chemicals, Inc. 2,2 bis(ethylferrocenyl)propane (C.sub.27 H.sub.32 Fe.sub.2). The cost of Catocene of about $250 per pound is based on the fact that it is a specialty chemical, manufactured in limited quantities, and it is difficult to prepare at the required level of purity. Catocene has functioned as a burning rate accelerator, but as a result of special problems associated with its use, another burning rate accelerator has been sought which does not contribute to the problem areas described below.
Catocene, because it is a liquid, migrates out of propellants. This loss of progressive reduction in the propellant's burning rate is a result of Catocene migration. One approach to preventing migration is establishing an equilibrium concentration of Catocene in the propellant and insulation. As a consequence of trying to establish this equilibrium condition, five times as much Catocene needs to be compounded into a liner as is incorporated into the propellant. As a result of the high Catocene content of the liner, in an effort to establish an equilibrium condition for the propellant, the liner ceases to be a true liner and will burn producing dense smoke. The dense smoke generated due to lack of oxidizer or oxygen (such as is present in the propellant), makes detection of the missile, while in flight, an easy task. The advantages of a burning rate accelerator which does not produce the above described undesirable results are readily recognized, especially for use in a tactical missile system where concealment is a necessity. Therefore, an object of this invention is to provide a solid explosive in a predetermined amount and of a predetermined pellet particle size for use in combination with solid composite propellant compositions to achieve ultrahigh burning rate.
Another object of this invention is to provide a burning rate accelerator which is compatible with typical solid composite propellant ingredients and which is readily ignited when embedded in the solid composite propellant composition.